Combustion apparatus

ABSTRACT

An improved solid fuel combustion apparatus intended for use in residential or light commercial settings capable of sustaining a controlled, continuous blue flame burn, resulting in high efficiency heat output with low emissions and low ash. The combustion apparatus is further capable of being thermostatically controlled, turning off combustion of the fuel when a desired temperature is reached and automatically re-igniting when more heat is called for, and also comprises improved safety features.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to devices suitable for burning solid fuel for heat and more particularly to wood burning combustion apparatuses intended for use in residential or light commercial settings. Such combustion apparatuses include wood stoves, wood fired boilers, and the like.

2. Description of Prior Art

Solid fuel burning combustion apparatuses are well-known in the art. Common examples include wood stoves and wood fired boilers. All such apparatuses operate on the following basic principles: solid fuel and combustion air (comprising oxygen) are ignited; some degree of gasification of the solid fuel occurs, resulting in the release of gases which mix with the combustion air to achieve further combustion; and the output of the combustion process is heat, unburned combustion gases, and particulates. Devices to achieve combustion of solid fuel may comprise one or more chambers in which the combustion occurs. They may utilize the natural flow of combustion air into the combustion chamber(s), or they may use forced introduction of combustion air into the combustion chamber(s) by electric fans, vacuum pumps, or other mechanical devices. They may involve the burning of the solid fuel with an upward oriented flame, or with a downward oriented flame (“down drafting”). They may employ heat exchangers to more efficiently utilize the heat generated by combustion in building heating systems.

Known solid fuel combustion apparatuses typically burn at temperatures between 900° F. and 1500° F. This is known as a “yellow flame” burn, as that is the primary color of the flame evident during combustion. At those temperatures, however, complete combustion is not possible, resulting in emissions of combustion gases and particulates, often in the form of visible smoke. These emissions are considered pollutants and are undesirable. Combustion involving a stabilized, continuous blue flame burn, which occurs at temperatures exceeding 2000° F., leads to much more complete combustion with a minimum of emissions. However, solid fuel combustion apparatuses intended for use in residential or light commercial settings known in the art cannot achieve consistent continuous blue flame burns.

Known solid fuel combustion apparatuses are also typically difficult to control, in that they need direct user attention to begin combustion, to monitor combustion, to end combustion, and to re-start combustion. This does not lend itself to thermostatic control, whereby the generation of heat is called for by an automatic device, such as a thermostat, in response to environmental conditions. Those devices that do employ thermostatic control typically do so with poor emissions and efficiency characteristics.

Known solid fuel combustion apparatuses are also typically less safe than other heating systems, due to the difficult to control combustion. This may lead to dangerous overheating with deleterious effect on any heating system to which the apparatus is connected.

Notwithstanding the above-described shortcomings of known solid fuel combustion apparatuses, there remains a need for alternatives to the burning of fossil fuels for heat. Wood burning combustion apparatuses use a renewable resource that often is less costly than oil, natural gas, or coal. Many individuals prefer the ability to obtain fuel domestically, often from their own land. There is thus a need to overcome the deficiencies of known solid fuel combustion apparatuses to improve their efficiency, safety, ease of use, and environmental impact.

It is therefore an objective of this invention to provide an improved combustion apparatus which achieves a consistent, continuous blue flame burn.

It is a further objective of this invention to provide an improved combustion apparatus which minimizes harmful emissions generated by the combustion process.

It is yet a further objective of this invention to provide an improved combustion apparatus which allows the automatic re-ignition of partially burned solid fuel.

It is yet a further objective of this invention to provide an improved combustion apparatus which may be thermostatically controlled by use of an automatic device such as a thermostat which causes a complete halt of combustion when heat is not called for and which causes a re-start of combustion when heat is called for.

It is yet a further objective of this invention to provide an improved combustion apparatus which comprises safety features to prevent damage to either itself or a heating system to which the apparatus is connected.

It is yet a further objective of this invention to provide an improved combustion apparatus which is easy and cost efficient to manufacture.

Other objectives of this invention will be evident from the following disclosure.

SUMMARY

The present invention is directed to an improved combustion apparatus for burning solid fuel, namely wood, for purposes of providing heat. The present invention is suitable for residential or light commercial use, and indoor or outdoor use. It is intended to be integrated with existing heating systems and is capable of safe automatic shutdown and automatic re-ignition after an extended shutdown period.

The apparatus employs initial combustion and gasification of solid fuel in a primary combustion chamber and a secondary combustion in a secondary combustion chamber. Measured amounts and distribution of pre-heated primary and secondary combustion air is provided via an oxygen introduction mechanism and a pressurizing mechanism, resulting in a controlled, self-sustaining continuous blue flame secondary combustion in the secondary combustion chamber. The resulting superheated exhaust gases have extremely low particulate emissions and a very limited amount of granular ash is produced.

The primary combustion chamber of the combustion apparatus includes a fuel loading, storage, and drying area that lies above a primary combustion zone. The primary combustion zone is found in the lower portion of the primary combustion chamber and is divided into a gasification region having substoichiometric air and a char fuel bed located at the bottom of the primary combustion chamber. The char fuel bed is created from an initial preparatory burn of the solid fuel and builds up from the floor of the primary combustion chamber to a height proximate to the point of introduction of oxygen into the primary combustion chamber by the oxygen introduction mechanism.

Once the char fuel bed is created, the combustion gases generated by gasification of the solid fuel, in combination with ongoing combustion of the char fuel, are mixed with a measured amount of pre-heated combustion air introduced by the oxygen introduction mechanism and pressurized by the pressurizing mechanism, resulting in a stabilized initial combustion in the primary combustion chamber. Then the gases, under continuous positive pressure, pass through a permeable divider into the secondary combustion chamber, where they undergo turbulent high temperature mixing with an additional amount of measured pre-heated combustion air introduced by the oxygen introduction mechanism into the secondary combustion chamber. The resultant automatic ignition and secondary combustion is a high temperature stabilized continuous blue flame, generating very high heat energy and minimal particulates.

The heated gases then pass out of the secondary combustion chamber via an exhaust structure and across a heat exchanger. The heat exchanger extends along the bottom and back of the insulated housing of the combustion apparatus, below and behind the combustion chambers, such that the heated gases must move in a downward direction for at least a portion of the distance between the secondary chamber and the heat exchanger. The heat exchanger extracts the maximal amount of heat energy from the heated combustion gases before the gases are exhausted via the exhaust structure.

A combination of high temperatures and an extended transit time of the combustion gases from the primary combustion chamber to the secondary combustion chamber, together with measured amounts of supplemental oxygen in the secondary combustion chamber, allow for virtually complete combustion of the solid fuel, yielding an extremely clean, smokeless burn. The extended transit time is provided by the depth and density of the char fuel bed and the gas flow resistance of the divider between the primary and secondary combustion chambers. A limit on the absolute air flow into the primary and secondary combustion chambers also controls the overall combustion rate and the transit time of the combustion gases. The rate of fuel combustion is substantially constant, dictated by the fixed amount of combustion airflow and the ratio of primary and secondary combustion airflows.

The combustion chambers and divider are constructed at least in part of a durable material having the properties of absorbing and retaining high levels of heat energy. This allows the combustion apparatus to be thermostatically controlled. By controlling the amounts of combustion air allowed into the combustion chambers, combustion can be initiated and halted. When the supply of combustion air is discontinued, combustion of the solid fuel ceases completely. However, the heat energy absorbed by the material comprising the combustion chambers and divider maintains the internal temperature of the combustion chambers well above the flash point temperature of the solid fuel for an extended period of time. Upon the reintroduction of combustion air into the super-heated combustion chambers the solid fuel and combustion gases automatically re-ignite and combustion continues. The introduction and discontinuation of combustion air into the combustion chambers may be controlled by a thermostat, thus allowing the combustion apparatus to maintain an ease of operability similar to oil or gas fueled furnaces and boilers.

The present invention also employs several design features to improve the safety of its operation. A typical danger with wood fired heating systems is the uncontrolled provision of heat to a heat exchanger. If too much heat is provided to a heat exchanger, for example during a power failure whereby the heat exchange medium within the heat exchanger (typically a liquid) stops circulating, the heat exchanger may overheat and the heat exchange medium contained therein may pressurize beyond the capability of the heat exchanger to contain it, causing a rupture of the system and a potential danger to any bystanders. The present invention minimizes the potential of overheating the heat exchanger by setting the default state of the apparatus to prevent introduction of combustion air into the combustion chambers. Thus, if there is a power interruption, the apparatus is designed to automatically cut off combustion air from the combustion chambers, causing further combustion to cease. As no further heat energy is added into the system, the heat exchanger does not receive additional heat energy and further dangerous pressurization of the heat exchange medium does not occur. Another design feature requires the heated exhaust gases to travel at least in part in a downward direction from the combustion chambers to the heat exchanger. Upon a power failure, the apparatus will cease providing the forces necessary to move the exhaust gases downward, so the hot gases will naturally rise and thus be prevented from reaching the heat exchanger. An additional feature of the present invention is a direct communication between the primary combustion chamber and the exhaust structure, controlled by a bypass damper. The bypass damper is designed to be opened when the access door to the primary combustion chamber is opened and to be closed when the access door to the primary combustion chamber is closed, thereby automatically releasing hot combustion gases out of the combustion chambers when a user accesses the primary combustion chamber, preventing a flash ignition in the primary combustion chamber. These safety features represent improvements over the known art in the safe operation of the apparatus.

Other features and advantages of the invention are described below.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective front view of the present invention.

FIG. 2 is an identical view of the present invention as shown in FIG. 1, with the outer walls of the housing and insulation removed to depict the underlying structures.

FIG. 3 is a cut-away perspective view of the present invention, depicting portions of the combustion chambers.

FIG. 4 is an identical view of the present invention as shown in FIG. 3, with portions of the outer walls of the combustion chambers removed to depict the interior structures thereof.

FIG. 5 is a perspective rear view of the present invention.

FIG. 6 is an identical view of the present invention as shown in FIG. 5, with the outer walls of the housing and insulation removed to depict the underlying structures.

FIG. 7 is a cut-away view of the present invention as shown in FIG. 6, depicting the relationship of the heat exchanger to the combustion chambers.

FIG. 8 is side section view of the present invention.

FIG. 9 is a perspective section view of the present invention.

FIG. 10 is a side plan view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The combustion apparatus 1 of the present invention is comprised of an insulated housing 10, a primary combustion chamber 20, a secondary combustion chamber 22, a divider 30 disposed between and separating the primary and secondary combustion chambers 20,22, an oxygen introduction mechanism 40, a pressurizing mechanism 50, and an exhaust structure 60.

The housing 10 of the present invention is constructed of a heavy-duty metallic material, such as steel or cast iron, though other materials may also be used. It comprises insulation within its interior sufficient to allow for safe contact of the outer surface during operation of the combustion apparatus 1. The housing 10 defines an internal space in which the other elements are located, though portions of the pressurizing mechanism 50 and the exhaust structure 60 extend outside the housing 10. See FIGS. 1, 5, 8, 9, and 10. One or more access doors 80 may be provided to allow access into the interior of the housing 10. See FIGS. 1, 8, and 10.

The primary combustion chamber 20 is a contained space located within the housing 10, suitably adapted to contain a quantity of solid fuel 5 and gases and to allow for the combustion of the fuel 5 and gases. See FIGS. 2, 3, 7, 8 and 9. The primary combustion chamber 20 may have separate walls defining the contained space, or the contained space may be defined by the walls of the housing 10, or by a combination thereof. In the preferred embodiment the primary combustion chamber 20 occupies most of the interior of the housing 10. The secondary combustion chamber 22 is a contained space located within the housing 10, suitably adapted to contain gases and to allow for the combustion of gases. See FIGS. 2, 3, 4, 8, and 9. The secondary combustion chamber 22 may have separate walls defining the contained space, or the contained space may be defined by the walls of the housing 10, or by a combination thereof. In the preferred embodiment the secondary combustion chamber 22 has a substantially smaller interior than that of the primary combustion chamber 20. See FIGS. 3 and 8. The secondary combustion chamber 22 is located adjacent to the primary combustion chamber 20 and is separated from the primary combustion chamber 20 by the divider 30. See FIG. 8. While the primary and secondary combustion chambers 20,22 may have any orientation with respect to each other, for example, they may be placed side by side, in the preferred embodiment the primary combustion chamber 20 is oriented above the secondary combustion chamber 22, with the divider 30 forming the floor of the primary combustion chamber 20 and the roof of the secondary combustion chamber 22. The region of the secondary combustion chamber 22 adjacent to the divider 30 is the burn region 24. See FIG. 8. In the preferred embodiment having a vertical orientation of the combustion chambers 20,22, the burn region 24 of the secondary combustion chamber 22 is located directly beneath the divider 30. The divider 30 is gas permeable, so that gases may pass from the primary combustion chamber 20 into the secondary combustion chamber 22. The primary and secondary combustion chambers 20,22, in combination, contain all combustion activities during operation of the combustion apparatus 1.

One or more of the housing's 10 access doors 80 allow access into the primary combustion chamber 20, and one or more of the housing's 10 access doors 80 allow access into the secondary combustion chamber 22. Fuel 5 may be loaded into the primary combustion chamber 20 through the access doors 80, and residue from combustion, such as fine ash, may be removed from the combustion chambers 20,22 through the access doors 80.

The divider 30 between the primary and secondary combustion chambers 20,22 has a first surface 32 located within the primary combustion chamber 20, a second surface 34 located within the secondary combustion chamber 22, and at least one aperture 36 passing completely through it from the first surface 32 to the second surface 34, resulting in the primary combustion chamber 20 and the secondary combustion chamber 22 being in communication with each other through the aperture or apertures 36. See FIGS. 4, 8, and 9. The divider 30 must be constructed of a material suitably adapted to absorb and retain heat energy at temperatures exceeding the flash point of the fuel 5. Exemplary materials for the divider 30 may be cast iron or stainless steel. However, in the preferred embodiment, the divider 30 is constructed of a castable refractory ceramic material. Castable refractory ceramic is both durable and has the ability to retain heat energy for an extended period of time. The longer that the temperature within the combustion chambers 20,22 is maintained above the flash point of the fuel 5, the longer the period of time the combustion apparatus 1 can re-ignite the fuel 5 after cessation of combustion.

The divider 30 may have any shape or configuration suitable for separating the primary and secondary combustion chambers 20,22, as described above. In one embodiment the divider 30 may be formed of a plurality of intersecting rods, forming a grate. In another embodiment the divider 30 may be a single planar member having one or more apertures formed through it. In the preferred embodiment of the present invention, the divider 30 is comprised of multiple elongated rectangular bricks 38 placed side by side, each brick 38 placed proximate to another brick 38 such that a gap exists between the pair, with each gap representing an aperture 36 of the divider 30. See FIGS. 4, 8, and 9. The gaps between the bricks 38 should be relatively narrow, between one eighth inch and two inches. The bricks 38 themselves may be of any suitable thickness, though it is recommended that they have a thickness of between two and ten inches. The thicknesses across all bricks 38 should be substantially uniform. In the preferred embodiment the sides of the bricks 38 are somewhat tapered in a downward direction, so that the gaps between pairs of bricks 38 widen from the first surface 32 of the divider 30 to the second surface 34 of the divider 30. In the most preferred embodiment the bricks 38 are constructed of castable refractory ceramic.

Both the primary combustion chamber 20 and the secondary combustion chamber 22 may be lined with castable refractory ceramic material. In the preferred embodiment the primary combustion chamber 20 is lined along one or more of its vertical walls for a portion of the height of those walls, beginning from the bottom of the chamber 20 and extending upwards, and the secondary combustion chamber 22 is lined along one or more of its vertical walls, beginning from the top of the chamber 22 and extending downwards. See FIGS. 3, 4, 7, and 8. Use of castable refractory ceramic liners 26 in the combustion chambers 20,22 increases the overall amount of heat energy which may be absorbed and retained by the combustion apparatus 1, thereby extending the amount of time that automatic re-ignition can occur. In the most preferred embodiment of the present invention, using a divider 30 and chamber liners 26 constructed of castable refractory ceramic, re-ignition of the fuel 5 has been achieved more than forty-eight hours after cessation of combustion.

The oxygen introduction mechanism 40 of the present invention is suitably adapted to direct oxygen into the primary and secondary combustion chambers 20,22 in a controlled manner. See FIGS. 6, 9 and 10. In the preferred embodiment the oxygen introduced into the combustion chambers 20,22 is a component of ambient air, though it is contemplated that pure oxygen or oxygen mixed with other gases could also be used. The oxygen introduction mechanism 40 comprises duct work 48 and at least one primary inlet 42 and at least one secondary inlet 44 attached to the duct work 48. See FIGS. 2, 6, 8, 9, and 10. In the preferred embodiment the duct work 48 is located substantially exterior to the primary combustion chamber 20, with a portion of the duct work 48 located within the secondary combustion chamber 22. In the most preferred embodiment, at least a portion of the duct work 48 is situated proximate to each access door 80. See FIG. 2. This causes combustion air passing through the duct work 48 to absorb heat energy from the access doors 80, preheating the combustion air for improved combustion efficiency, while also cooling the access doors 80.

A controlled amount of combustion air (comprised at least in part of oxygen) travels through the duct work 48 and through the primary and secondary inlets 42,44. In the preferred embodiment the amount of combustion air passing through the primary inlets 42 and the secondary inlets 44, respectively, is controlled by the length of duct work 48 the combustion air must pass through before arriving at the respective inlets 42,44, in combination with the gas flow resistance of said ductwork 48 and inlets 42,44. An additional or alternate mechanism for controlling the combustion air passing through the oxygen introduction mechanism 40 involves the use of one or more dampers 46 situated within the duct work 48 of the oxygen introduction mechanism 40. See FIGS. 6 and 10. Each damper 46 is suitably adapted to be positioned in either an open position or a closed position, such that the open position of a damper 46 permits combustion air to pass through one or more of the inlets 42,44 and the closed position of a damper 46 prevents combustion air from passing through one or more of the inlets 42,44. In the most preferred embodiment a single damper 46 is adapted to control the passage of combustion air through all of the inlets 42,44. When the damper 46 in this most preferred embodiment is in the closed position no additional combustion air is permitted into either the primary combustion chamber 20 or the secondary combustion chamber 22, thereby causing combustion to completely cease. When the damper 46 in this most preferred embodiment is in the open position combustion air is introduced into the combustion chambers 20,22 permitting initial ignition or re-ignition of the solid fuel 5 and continued combustion thereof.

In the preferred embodiment the damper or dampers 46 of the oxygen introduction mechanism 40 are suitably adapted to automatically be positioned to the closed position when operation of the combustion apparatus 1 must cease due to unsuitable environmental conditions. This stops combustion, thereby preventing the buildup of heat in the system. Each damper 46 comprises a gravity-based mechanism which disposes the damper 46 to the closed position. Alternatively, a spring mechanism may be used to dispose the damper 46 to the closed position. The flow of combustion air, controlled by the pressurizing mechanism 50, is sufficient to overcome the force of gravity on the damper 46 and disposes the damper 46 to the open position. During adverse environmental conditions, such as overheating, the pressurizing mechanism 50 can be stopped to completely halt the flow of combustion air into the duct work 48, whereby gravity returns the damper 46 to the closed position. A loss of power to the combustion apparatus 1, which could cause damage to the heating system if heat were to continue to be generated, would also stop the pressurizing mechanism 50 from causing air to flow into the duct work 48, achieving the same result and a complete cessation of combustion. Alternatively, the damper or dampers 46 can be mechanically positioned to the closed position, by a manual lever or by an actuator.

The primary inlet or inlets 42 are located in the primary combustion chamber 20 and are oriented to direct oxygen onto fuel 5 placed into the primary combustion chamber 20. In the preferred embodiment there are multiple primary inlets 42, with the primary inlets 42 disposed along at least two of the side walls of the primary combustion chamber 20. See FIGS. 3 and 4. In the most preferred embodiment the primary inlets 42 are apertures formed through the liners 26 of the primary combustion chamber 20, the apertures of the primary inlets 42 being in communication with the duct work 48. See FIGS. 2, 3, 4, 7, and 9. In other embodiments the primary inlets 42 may be metal nozzles depending from the duct work 48 and extending into the interior of the primary combustion chamber 20. The primary inlets 42 should all be substantially the same distance from the floor of the primary combustion chamber 20, with the preferred distance being between one inch and fourteen inches from the floor.

The secondary inlet or inlets 44 are located in the secondary combustion chamber 22 and are oriented to direct oxygen into the burn region 24 of the secondary combustion chamber 22. In the preferred embodiment there are multiple secondary inlets 44, and in the most preferred embodiment the secondary inlets 44 are apertures formed bi-laterally into a horizontal extension of the duct work 48 located within the secondary combustion chamber 22 proximate to the divider 30. See FIG. 8. The preferred distance between the secondary inlets 44 and the second surface 34 of the divider 30 is between one and three inches. Other embodiments of the secondary inlets 44 are also contemplated, for example metal nozzles depending from the duct work 48 and extending into the interior of the secondary combustion chamber 22.

The pressurizing mechanism 50 of the present invention is suitably adapted to supply positive pressure to the primary combustion chamber 20 to create a pressure differential between the gases contained in the primary combustion chamber 20 and the gases contained in the secondary combustion chamber 22, such that the gases contained in the primary combustion chamber 20 are at a higher pressure relative to the gases contained in the secondary combustion chamber 22. The pressure differential must be sufficient to cause gases contained in the primary combustion chamber 20 to flow through the aperture or apertures 36 of the divider 30 into the secondary combustion chamber 22. In the most preferred embodiment, the pressure differential is between 0.005 and 0.030 inches of mercury as measured by the difference in pressures between the maximal values of the primary inlet or inlets 42 and secondary inlet or inlets 44. During combustion this pressure differential causes the flow of combustion gases through the divider 30 in a downward direction, resulting in a downward burn in the burn region 24 of the secondary combustion chamber 22.

The pressurizing mechanism 50 may comprise any means for generating positive pressure to create the required pressure differential. In the preferred embodiment the pressurizing mechanism 50 comprises a low power electric fan. See FIG. 10. It is contemplated that such a fan would operate on standard alternating current. The combustion apparatus 1 may comprise a backup power source to provide electricity to the pressurizing mechanism 50 in the event of an interruption in a primary source of power to the pressurizing mechanism 50, for example, a battery. In the most preferred embodiment the pressuring mechanism is integrated with the oxygen introduction mechanism 40, whereby the electric fan supplies air directly into the duct work 48 of the oxygen introduction mechanism 40. A shorter length of duct work 48 supplying the primary inlets 42 than the length of duct work 48 supplying the secondary inlets 44, in combination with the gas flow resistance of said ductwork 48 and inlets 42,44, allows a single fan to create the required differential pressure. In other embodiments, multiple fans may be used, with a more powerful fan supplying combustion air to the primary combustion chamber 20 and a less powerful fan supplying combustion air to the secondary combustion chamber 22. In yet other embodiments, multiple fans may supply combustion air to each chamber. In any of the foregoing embodiments, the required pressurization is achieved by the one or more fans causing a greater quantity of combustion air to be introduced into the primary combustion chamber 20 than into the secondary combustion chamber 22 for a given period of time. Other embodiments of the pressurizing mechanism 50 are also contemplated, such as air pumps in connection with the primary combustion chamber 20. In yet other embodiments the pressurizing mechanism 50 may be separate from the oxygen introduction mechanism 40.

The combustion apparatus 1 may comprise a thermostatic control device, such as a thermostat. The thermostatic control device must be suitably adapted to control the combustion of fuel 5 and gases contained within the combustion apparatus 1, such that when the thermostatic control device calls for heat fuel 5 and gases within the combustion apparatus 1 are burned and when the thermostatic control device does not call for heat the burning of fuel 5 and gases within the combustion apparatus 1 ceases. This thermostatic control of combustion makes the combustion apparatus 1 more convenient to use and better regulates the ability of the combustion apparatus 1 to provide only desired amounts of heat to a heating system. This in turn yields better fuel efficiency. In the preferred embodiment, the thermostatic control device controls the operation of the oxygen introduction mechanism 40, such that thermostatic control is achieved by depriving oxygen to extinguish combustion, and re-introducing oxygen to re-ignite combustion. No separate energy source is needed to re-ignite combustion, because the temperature within the combustion chambers 20,22 is above the flash point of the fuel 5. In this embodiment, when the thermostatic control device calls for heat the thermostatic control device positions the damper or dampers 46 of the oxygen introduction mechanism 40 to the open position, allowing combustion air to be introduced into the combustion chambers 20,22, and when the thermostatic control device does not call for heat the thermostatic control device positions the damper or dampers 46 of the oxygen introduction mechanism 40 to the closed position, preventing further introduction of combustion air into the combustion chambers 20,22. In the most preferred embodiment, the use of a thermostatic control device in conjunction with the use of castable refractory ceramic material for the divider 30 and combustion chamber liners 26 ensures efficient extinguishment and re-ignition of combustion on an as-needed basis.

The exhaust structure 60 of the present invention is suitably adapted to remove heated gases from the secondary combustion chamber 22. It has a connection end 62 in communication with the secondary combustion chamber 22, and a chimney which vents outside the housing 10 of the combustion apparatus 1. See FIGS. 3, 4, 5, 6, 7, 8, and 10.

The combustion apparatus 1 may further comprise a bypass damper 90. See FIGS. 3, 4, 7, 8, and 9. The bypass damper 90 forms a closable communication between the primary combustion chamber 20 and the exhaust structure 60. The bypass damper 90 is suitably adapted to be positioned in either an open position or a closed position, such that when in the open position the bypass damper 90 permits gases to pass from the primary combustion chamber 20 directly into the exhaust structure 60 and when in the closed position the bypass damper 90 prevents direct communication between the primary combustion chamber 20 and the exhaust structure 60. The bypass damper 90 is further adapted to be positioned in its open position whenever an access door 80 to the primary combustion chamber 20 is opened. This safety feature allows the venting of combustion gases to reduce the risk of a flash ignition when an access door 80 is opened.

The combustion apparatus 1 may also comprise a heat exchanger 70. See FIGS. 4, 7, 8, and 9. In the preferred embodiment the heat exchanger 70 is in communication with the exhaust structure 60. In the most preferred embodiment the heat exchanger 70 is contained within the exhaust structure. High temperature gases exiting the secondary combustion chamber 22 via the exhaust structure 60 pass over the heat exchanger 70, which in turn removes heat energy from the gases and delivers that heat energy to a heating system. Heat exchangers are well known in the art, and any style heat exchanger may be used with the present invention. In the preferred embodiment the heat exchanger 70 comprises closed loops of piping which contain a heat exchange medium, preferably a liquid, though a gaseous heat exchange medium is also contemplated. The heat exchange medium absorbs heat energy from the heated gases, then is circulated through the closed loop piping where it releases heat energy into a heating system. The heat exchange substance may be circulated by means of a circulating pump, as is well known in the art.

In the preferred embodiment the heat exchanger 70 is located within the housing 10 but remotely from the secondary combustion chamber 22 in such a manner that heated gases moving from the secondary combustion chamber 22 via the exhaust structure 60 to the heat exchanger 70 must move at least partially in a downward direction prior to reaching the heat exchanger 70. This is a safety feature, since the failure of a circulating pump could prevent the heat exchange medium from releasing heat energy, and an uncontrolled buildup of heat energy in the heat exchange medium could lead to a rupture of the closed loop piping. Moving the heated gases in a downward direction can only be achieved by applying a force to the gases, for example, the pressure differential created by the pressurizing mechanism 50 is sufficient to move the gases downward. However, upon a power failure, which would disable the circulating pump, the pressurizing mechanism 50 would also cease pressurizing the system, causing the damper or dampers 46 of the oxygen introduction mechanism 40 to return to the closed position, completely halting combustion. This prevents more heat energy from being created, and the heated gases already in the combustion apparatus 1 will naturally rise, moving away from the heat exchanger 70. This dual safety design greatly reduces the risk of an undesirable overheating of the heat exchange medium of the heat exchanger 70.

In the most preferred embodiment the heat exchanger 70 runs horizontally along the bottom of the housing 10, beneath the secondary combustion chamber 22, and then extends vertically along the rear of the housing 10. See FIGS. 7 and 8. The extended length of the heat exchanger 70 permits the heated gases to give up more heat energy as they pass over the heat exchanger 70 and are vented. This improves the overall efficiency of the system, allowing more heat to be extracted and less to be wasted as heated exhaust gases.

The initial combustion of the solid fuel 5 occurs in the lower portions of the primary combustion chamber 20. Combustion air combines with combustion gases released from the fuel 5 to feed the combustion process. A char fuel bed 7 is created from an initial preparatory combustion. The char fuel bed 7 is created from the lowest portions of the fuel 5 located at the bottom of the primary combustion chamber 20. The top of the char fuel bed 7 is proximate to the primary inlets 42 of the oxygen introduction mechanism 40. Gasification of the solid fuel 5 occurs above the char fuel bed 7, releasing combustion gases which are burned in the initial combustion; these gases are then forced downward by the pressure differential through the char fuel bed 7 and through the apertures 36 of the divider 30 into the secondary combustion chamber 22, becoming superheated in the process. The addition of a controlled amount of combustion air into the burn region 24 of the secondary combustion chamber 22 causes the superheated combustion gases to re-ignite in the burn region 24 of the secondary combustion chamber 22, resulting in secondary burn achieving an extremely hot, clean, continuous blue flame. As a result of the two burns, the exhaust gases are extremely hot, reaching temperatures in excess of 2000° F., with very little particulate matter remaining. The gases then move past the heat exchanger 70 where heat energy is released into the heating system, and are then exhausted.

Modifications and variations may be made to the disclosed embodiments of the present invention without departing from the subject or spirit of the present invention as defined in the following claims. 

1. A combustion apparatus comprising a primary combustion chamber, said primary combustion chamber suitably adapted to contain a quantity of solid fuel and to contain gases; a secondary combustion chamber, said secondary combustion chamber located adjacent to the primary combustion chamber and having a burn region located proximate to the primary combustion chamber, said secondary combustion chamber suitably adapted to contain gases; a divider disposed between and separating the primary combustion chamber and the secondary combustion chamber, said divider having a first surface located within the primary combustion chamber, a second surface located within the secondary combustion chamber, and at least one aperture passing completely through said divider from the first surface to the second surface such that the primary combustion chamber and the secondary combustion chamber are in communication with each other through said at least one aperture, said divider constructed of a material suitably adapted to absorb and retain heat energy at temperatures exceeding the flash point of said fuel; an oxygen introduction mechanism suitably adapted to direct measured amounts of oxygen into the primary combustion chamber in a controlled manner and measured amounts of oxygen into the secondary combustion chamber in a controlled manner; a pressurizing mechanism suitably adapted to supply positive pressure to the primary combustion chamber to create a pressure differential between the gases contained in the primary combustion chamber and the gases contained in the secondary combustion chamber such that the gases contained in the primary combustion chamber are at a higher pressure relative to the gases contained in the secondary combustion chamber; and an exhaust structure, having a connection end in communication with the secondary combustion chamber, said exhaust structure suitably adapted to remove heated gases from the secondary combustion chamber; wherein a first burn of the fuel occurs in the primary combustion chamber creating combustion gases and a char fuel bed, the combustion gases are forced through the char fuel bed and through the at least one aperture of the divider into the secondary combustion chamber as a result of the pressure differential between the gases contained in the primary and secondary combustion chambers, a second burn of the combustion gases occurs in the burn region of the secondary combustion chamber, and superheated gases are exhausted out of the secondary combustion chamber through the connection end of the exhaust structure.
 2. The combustion apparatus of claim 1 wherein the second burn of the combustion gases occurring in the burn region of the secondary combustion chamber is a controlled, sell-sustaining, continuous blue flame burn, resulting in the fully combusted combustion gases achieving temperatures of at least 1600° F.
 3. The combustion apparatus of claim 1 wherein the divider is constructed of a castable refractory ceramic material.
 4. The combustion apparatus of claim 1 wherein the divider further comprises a multiplicity of bricks, each said brick being constructed of castable refractory ceramic material, said bricks placed proximate to each other such that at least one gap exists between at least one pair of bricks forming an aperture of the divider.
 5. The combustion apparatus of claim 1 wherein the oxygen introduction mechanism comprises duct work, said duct work suitably adapted to convey oxygen; at least one primary inlet, each said primary inlet in communication with the duct work, each said primary inlet located in the primary combustion chamber and oriented to direct oxygen onto fuel placed into the primary combustion chamber; and at least one secondary inlet, each said secondary inlet in communication with the duct work, each said secondary inlet located in the secondary combustion chamber and oriented to direct oxygen into the burn region of the secondary combustion chamber.
 6. The combustion apparatus of claim 5 wherein the oxygen introduction mechanism further comprises at least one damper, each said damper suitably adapted to be positioned in either an open position or a closed position, such that the open position of each said damper permits oxygen to pass through one or more of said primary and secondary inlets and the closed position of each said damper prevents oxygen from passing through one or more of said primary and secondary inlets.
 7. The combustion apparatus of claim 6 wherein each of the at least one damper of the oxygen introduction mechanism is further suitably adapted to automatically be positioned in the closed position when operation of the combustion apparatus must cease due to unsuitable environmental conditions, such that in the event of unsuitable environmental conditions the oxygen introduction mechanism ceases to direct oxygen into either the primary combustion chamber or the secondary combustion chamber.
 8. The combustion apparatus of claim 6 wherein the pressurizing mechanism is powered by electricity and each of the at least one damper of the oxygen introduction mechanism is further suitably adapted to automatically be positioned in the closed position when electric power to the pressurizing mechanism is interrupted, such that in the event of a power interruption to the pressurizing mechanism the oxygen introduction mechanism ceases to direct oxygen into either the primary combustion chamber or the secondary combustion chamber.
 9. The combustion apparatus of claim 8 further comprising a backup power source to provide electricity to the pressurizing mechanism in the event of an interruption in a primary source of power to the pressurizing mechanism.
 10. The combustion apparatus of claim 6 further comprising a thermostatic control device, said thermostatic control device being suitably adapted to control the operation of the oxygen introduction mechanism such that when the thermostatic control device calls for heat the thermostatic control device positions each of the at least one damper of the oxygen introduction mechanism in the open position and when the thermostatic control device does not call for heat the thermostatic control device positions each of the at least one damper of the oxygen introduction mechanism in the closed position.
 11. The combustion apparatus of claim 5 further comprising at least one access door, each said access door providing access into either the primary combustion chamber or the secondary combustion chamber, wherein at least a portion of the duct work is situated proximate to at least one said access door.
 12. The combustion apparatus of claim 1 wherein the pressurizing mechanism comprises at least one fan suitably adapted to move air into the primary and secondary combustion chambers.
 13. The combustion apparatus of claim 1 wherein the pressurizing mechanism is integrated with the oxygen introduction mechanism.
 14. The combustion apparatus of claim 1 further comprising a heat exchanger, said heat exchanger being in communication with the exhaust structure.
 15. The combustion apparatus of claim 14 wherein the heat exchanger is located remotely from the secondary combustion chamber in such a manner that heated gases moving from the secondary combustion chamber through the exhaust structure to the heat exchanger must move at least partially in a downward direction prior to reaching the heat exchanger.
 16. The combustion apparatus of claim 1 further comprising a thermostatic control device, wherein said thermostatic control device is suitably adapted to control combustion of fuel and gases contained within the combustion apparatus such that when the thermostatic control device calls for heat fuel and gases within the combustion apparatus are burned and when the thermostatic control device does not call for heat the burning of fuel and gases within the combustion apparatus ceases.
 17. The combustion apparatus of claim 16 wherein the thermostatic control device controls the operation of the oxygen introduction mechanism.
 18. The combustion apparatus of claim 1 further comprising at least one access door, each said access door providing access into either the primary combustion chamber or the secondary combustion chamber, wherein at least one said access door provides access into the primary combustion chamber; and a bypass damper, said bypass damper forming a closable communication between the primary combustion chamber and the exhaust structure, said bypass damper suitably adapted to be positioned in either an open position or a closed position, such that the open position of said bypass damper permits gases to pass from the primary combustion chamber directly into the exhaust structure and the closed position of said bypass damper prevents direct communication between the primary combustion chamber and the exhaust structure; whereby said bypass damper is suitably adapted to be positioned in its open position whenever an access door to the primary combustion chamber is opened.
 19. The combustion apparatus of claim 1 further comprising a heat exchanger, said heat exchanger being in communication with the exhaust structure and located remotely from the secondary combustion chamber in such a manner that heated gases moving from the secondary combustion chamber through the exhaust structure to the heat exchanger must move at least partially in a downward direction prior to reaching the heat exchanger; and a thermostatic control device, wherein said thermostatic control device is suitably adapted to control combustion of fuel and gases contained within the combustion apparatus such that when the thermostatic control device calls for heat fuel and gases within the combustion apparatus are burned and when the thermostatic control device does not call for heat the burning of fuel and gases within the combustion apparatus ceases; wherein the divider is constructed of a castable refractory ceramic material; the oxygen introduction mechanism comprises at least one primary inlet, each said primary inlet located in the primary combustion chamber and oriented to direct oxygen onto fuel placed into the primary combustion chamber, and at least one secondary inlet, each said secondary inlet located in the secondary combustion chamber and oriented to direct oxygen into the burn region of the secondary combustion chamber; and the second burn of the combustion gases occurring in the burn region of the secondary combustion chamber is a controlled, self-sustaining, continuous blue flame burn, resulting in the fully combusted combustion gases achieving temperatures of at least 1600° F.
 20. The combustion apparatus of claim 1 further comprising a housing, said housing having an outer surface and an interior, and one or more access doors allowing access into the interior, said housing constructed of a heavy-duty metallic material and further comprising insulation within its interior sufficient to allow for safe contact of the outer surface during operation of the combustion apparatus; wherein said housing is suitably adapted to contain the primary combustion chamber, the secondary combustion chamber, the divider, the oxygen introduction mechanism, at least a portion of the pressurizing mechanism, and at least a portion of the exhaust structure. 